The subject of the present invention is a device for producing foam and the analysis of its properties together with a method for execution of a foam analysis.
Foams occur in different applications. Apart from foodstuffs (beer foams, fruit juice foams) they are also relevant in the manufacture of cosmetics and for technological applications (e.g. cleaning of parts). For evaluation of foams it is necessary to know the characterising parameters of the foam and its changes over time. In particular, these parameters are the height of the foam, the liquid-foam interface, the sizes and shape of the pores as well as the variation of these characteristics over time.
A series of possibilities for determining these parameters is known from the state of the art.
A sensor for measuring turbidity and the proportion of foam of a washing or rinsing liquid is known from DE 20 022 433 U1. The sensor directs the light of a light-emitting diode on an interface to the medium to be examined. Depending on the liquid adjacent to this interface and its refractive index, the light is diffused into the liquid or back into the sensor body. The amount of back-scattered light allows a statement to be made of the parameters to be determined. The sensor only permits a rough qualitative statement on the foam at the spatially restricted interface.
EP 2 418 315 A2 proposes to use the degree of attenuation of the light passing through an optical conductor which is surrounded by the washing liquid, possibly with a proportion of foam, for measuring the liquid-foam interface or to determine the proportion of foam. Here also, the attenuation of the light is due to the different refractive index at the interface of the optical conductor/medium used for detection. A disadvantage is that the optical conductor must pass directly into the medium here.
WO 2005/003758 A1 proposes to determine the image of foam in a test vessel with an electronic image recording device, e.g. a CCD camera. The foam structure is then evaluated by detecting the pore walls in the image and determining characteristic properties, here the fractal dimension of the pore images. The problem here is that, with many foams which form transparent pore surfaces, the walls of pores which connect to the front walls of the pores at the depth of the foam, are incorrectly recognised by the evaluation electronics as frontal walls. This leads to a falsification of the measurement result.
EP 2 950 081 A1 describes an apparatus for foam analysis. The device has two prismatic components which overlap one another so that they form a common base portion and are so arranged that an incident beam on the entry side of the first prism passes through the base portion to the plane, transparent surface of a pressure vessel with foam. If the light beam encounters a surface area on which the cavity of a foam bubble is in contact, the light is totally reflected. Otherwise, it is deflected into the foam. The totally reflected beam emerges through the exit side of the second prism and is detected by a camera. A disadvantage of this design is that only a limited area of the foam can be examined. Furthermore, the design is complex, due to the complicated integration of the base area of the prisms into the pressure chambers, and is not suitable for a rapid change of sample. Moreover, due to the attachment of prisms, the original measurement vessel geometry is disrupted and thus the foam formation characteristic is changed as compared with the original measurement vessels.